Extended addressing using sub-addressed segment registers

Abstract From the Canadian patent

A selected address within one of two segments of a memory space of a second address/data bus can be, accessed from a first bus through one of two data registers. In addition, the location of the two segments within the memory space of the second bus is selectable through two segment registers, which are accessed from the first bus through the first data register. A two byte wide "mode" register, which can be directly accessed from the first bus, stores data within three ranges. When the mode register data is within the first range a, selected segment register can be accessed through the first data register. A first value within this range selects the first segment register, while a second …